Gas lift apparatus and system



H- U. GARRETT GAS LIFT APPARATUS AND SYSTEM March 12, 1968 Filed April 6, 1966 I m f m m M M M W W rm Wm c am/% A III 6 ai r M x 111 m W i .M 2 8 5 0 5 a 2 4 a a w m a a W a 2 4/3/H A z 2 AK n \f\w n United States Patent 3,372,650 GAS LIFT APPARATUS AND YSTEM Henry U. Garrett, Longview, Tex. (2205 Lee St., Houston, Tex. 77025) Filed Apr. 6, 1966, Ser. No. 540,707 6 Claims. (Cl. 103--233) ABSTRACT OF THE DISiILOSURE This patent discloses a gas lift method and system using casing pressure-responsive valves for loading tubing pressure-responsive valves to unload a well, and using the tubing pressure-responsive valves to thereafter lift liquid from the well.

This invention relates to lifting of fluid in a well with gas, and more particularly to a new method, system and valve for gas-lifting of fluid.

There are many different types of gas-lift installations. Essentially, each system provides for U-tubing and gaslifting through downwardly spaced valves to unload the fluid in the well, and then gas-lifting through a lower valve for normal production of the well. This lower valve may be any of several valves in the lower section of the tubing, depending on well conditions, and the working valve may change with changing Well conditions.

It is conventional to unload a well with casing-responsive valves, that is, valves which are controlled primarily in response to changes in casing pressure. After the uppermost unloading valve is uncovered by U-tubing and fluid thereabove gas-lifted, the valve may be closed responsive to a reduced casing pressure and fluid is U-tubed and gas-lifted through the next lower valve. During normal production through the working valve, these unloading valves usually remain closed. This type of system provides for wide spacing of the unloading valves to reduce valve costs in an installation.

Another type of installation employs the tubing-responsive valve in which the valve opens and closes in response to changes in tubing pressure. This type of valve, which may be the well known conventional differential valve, provides a very definite advantage during normal gas-lifting of the well in that the pressure of the fluid in the tubing as it moves toward the surface may exert a sufiicient pressure on the tubing-sensitive valve to open the valve and permit injection of additional fluid through one or more of the Working valves. In order to accomplish this, the valve should be sensitive to a small load. For instance, in a differential valve this load preferably would be between 50 and 150 p.s.i. differential between casing and tubing pressure. This multiple-point injection, where gas is introduced through the working valve and through one or more of the unloading valves, introduces additional gas along the tubing string in accordance with tubing pressure demand to thus achieve optimum multiple-point injection.

The sensitive tubing-responsive valve has the decided disadvantage of requiring a relatively close spacing between valves Which are set to open at the desired 50 to 150 p.s.i., because the differential valve is only open during the time when the differential thereacross is between balance and this preferred setting of 50 to 150 psi. Thus, multiple-point injection is possible with tubing-responsive valves such as the differential valve, but the installations are costly as the valves must be positioned very close together.

It is an object of this invention to provide a system and a method of unloading and gas-lifting a well which utilizes tubing-responsive valves which may be very sensitive to tubing pressure such as a differential valve set to operate at a differential of 50 to 150 psi, in which the tubing- 3,372,650 relented Mar. 12, 1968 sensitive valves may be spaced as far apart as the conventional casing-sensitive valves.

Another object is to provide a method and system for unloading and gas-lifting a well in which tubing-sensitive valves are employed and are loaded by casing-sensitive valves so that they may be spaced as far apart as the casing-sensitive valves which load the tubing-sensitive valves.

Another object is to provide a method and system for unloading and gas-lifting a well which provides for multiple-point injection during gas lifting through unloading valves which are spaced as far apart as in a conventional casing-responsive installation.

Another object is to provide a system for unloading and gas-lifting a well in which differential-type unloading valves are employed which are spaced as far apart as conventional casing-responsive valves.

Another object is to provide a gas-lift system which utilizes tubing-responsive valves spaced as far apart as conventional casing-responsive valves, and which operates equally well in constant flow or intermittent lift wells.

Another object is to provide a method and system of unloading and gas-lifting a well which provides optimum performance with minimum information.

Another object is to provide a system and method of unloading and gas-lifting a well which gives excellent dual production performance without conflict between the multiple tubing strings. 1

Another object is to provide a method and system for gas-lifting a well which eliminates the need for a clock control or intermitter at the surface.

Another object is to provide a simple method and system for unloading and gas-lifting a. well which operates efliciently through a wide range of system pressures with the same installation in the well.

Another object is to provide a combination tubingsensitive and casing-sensitive valve in a single housing.

Another object is to provide a combination diflerential and casing-sensitive valve in a single housing.

Another object is to provide a combination mandrel, tubing-sensitive and casing-sensitive valve to practice the method and system of the objects set out above.

Other objects, features and advantages of the invention will be apparent from the specification, drawings and the claims.

In the drawings, where-in like reference numerals indicate like parts:

FIGURE 1 is a view partly in elevation and partly in cross-section through a well which illustrates the method and system of this invention;

FIGURE 2 is a view partly in elevation and partly in section through a combination casing-responsive and differential valve which may be employed in practicing the method and system of this invention.

Referring first to FIGURE 1, there is shown a well having a casing 10 with perforations 11 into the producing formation. Tubing 12 extends from the surface to the producing formation and, if desired, a suitable packer 12a may be positioned immediately above the producing formation in the conventional manner.

In accordance with this invention, a plurality of valves are positioned at spaced intervals along the tubing 12. One series of valves 13, which may be identical in construction, are responsive to tubing pressure. That is, they open and close primarily in response to the pressure in the tubing which is exerted on the valve. Preferably, these tubing-sensitive valves are differential valves and may be any conventional type of differential valve such as that shown in FIGURE 2. Thus, with the casing annulus subjected to pressure, as is conventional in gas lift operations, the several valves 13 will open and close in re sponse to tubing pressure.

As is well known, eflicient tubing-responsive valves should be very sensitive and should operate in a range of roughly 50 to 150 psi. if they are to be efiicient in multiplea oint injection. However, valves of such sen sitivity would be extremely expensive if used alone because they would have to be placed so close together that a large number of valves would need to be employed.

In order to be able to use tubing-sensitive valves for unloading valves and space them substantially the same spacing as casing-sensitive valves, there are provided a plurality of casing-sensitive valves 14 also spaced along the tubing. These casing-sensitive valves open in response to casing pressure and permit movement of gas and liquids from the casing into the tubing to increase the height of liquid in the tubing, and thus load the tubing-sensitive valves 13. With this purpose in mind, it will be apparent that the valves 13 and 14 should be located sufliciently close to each other that each valve 13 will be assured of being loaded by a casing valve 14.

Preferably, each pair of valves 13 and 14 are mounted on a single mandrel 15. However, valves 13a and 14a illustrate that the valves may be mounted on adjacent mandrels 16 and 17, it only bein necessary that the casing-responsive valve 14a be positioned such that it will load the tubing-responsive valve 13a with liquid so that the valve 13a will open.

In conventional wells using casing-responsive valves for unloading purposes, it is desirable that the port through the valve have a substantial size so that a substantial amount of gas may be injected into the tubing to raise the liquid. This type of valve has the disadvantage that the upper valves must be closed as the level of liquid in the casing is lowered. Otheiwise, the gas will pass through the upper valves to the surface without doing work. Conventionally, these valves are closed by stepping down the pressures as the level of liquid in the well is lowered. By using this system, the valves 14 may have very tiny ports and, if desired, all valves may remain open during the unloading cycle. Due to the tiny ports involved, the small amount of gas passing through an upper valve 14 after the liquid level has been lowered will not be objectionable. This will permit setting of the casing-responsive valves 14 at the same pressure so that only a single stepdown in pressure is necessary to close all of the casing responsive valves and use only the tubing-responsive valves during the normal gas-lifting of the well. Of course, the valves 14 may be stepped down, if desired.

From an operational standpoint, it will be presumed that the well is filled with liquid in both the tubing and casing up to the top of the well. The valves 13 may be differential valves, such as shown in FIGURE 2, and the valves 14 may be conventional bellows-operated valves, such as the bellows-operated valves shown internally of the differential valve of FIGURE 2. With the well under balanced conditions, the valves 14 will be closed and, assuming valves 13 to be the differential valves shown in FIGURE 2, the differential valve will be open. The controller 18 will be set to introduce lifting gas through the valve 19 and in accordance with conventional practice, this lifting gas may be under several hundred pounds of pressure, such as 800 psi. As this gas pressure enters the casing, it quickly builds up and the valve 13 and 14 are subject to this casing pressure plus, of course, the hydrostatic head of fluid above each valve. The hydrostatic pressure of fluid in the tubing is also exerted on each valve. Preferably, the tubing connects to a tank battery (no-t shown) in which little or no back pressure is exerted on the tubing.

As the casing pressure builds up, the differential valves 13 will be closed because there will be insufficient tubing pressure to open these valves.

As the casing pressure builds up the selected valve to open the casing-responsive valves 14, fluid will begin to U-tube through the valves 14 and rise in the tubing 12. When the pressure exerted by this rising column of fluid on the topmost valve 13 reaches a selected value, the differential valve will open. Fluid will U-tube through the differential valve 13 and, upon this valve being uncovered, that is, exposed to gas in the casing, the gas will enter the tubing and gas-lift liquid above this point from the well. As soon as the tubing has been cleared of liquid to a point where the necessary tubing pressure is not present, the differential valve will close.

The same sequence of operation will continue progressively down the tubing until the working valve is reached. This working valve may be one of several valves close to the bottom of the well and will depend upon the natural characteristics of the well.

During the unloading operation and during normal gas-lifting of the well, the tubing-responsive valves 13 may operate to provide for multiple-point injection. Thus, as a slug of fluid is rising through the tubing and passes a valve 13, it may exert a suflicient pressure on the valve to cause a particular valve to open. When this occurs, gas will be injected through such valve to assist in lifting the slug of liquid up the tubing.

As tubing-responsive valves alone are used during normal operation, a complex surface control ystem is not required. It is only required that a suitable pressure regulator valve 19 be provided, and, if desired, a controller 18 may be utilized to control the back pressure of valve 19. This simple surface system is possible because the valves 13 will open to inject gas into the tubing when, and only when, there is present a suitable column of liquid in the tubing to be lifted to the surface. This eliminates the need for time cycles and the like.

While mention is made above of the desirability of using a small-port valve 14, it is, of course, apparent that these ports do not have to be small, and the valves 14 could be closed as they are uncovered as by stepping down the pressure. They would still function to uncover the tubing-responsive valves 13 and these valves would function in the same manner.

Reference is now made to FIGURE 2 wherein a diflerential valve and casing-responsive valve are provided in one housing. This valve may be substituted for the valves 13 and 14.

The valve includes a housing 21 having a lower seat sub 22 and upper seat sub 23a. The lower seat sub is designed to be secured to a conventional mandrel.

A flowway 23 is provided through the housing having an outlet 24 for communication with the mandrel and one or more ports 25 which provide an inlet.

Flow of fluid through the flowway 23 is controlled by a valve seat 26 and a valve member 27 cooperative therewith. This is the valve member and seat of the differential or tubing-responsive valve. The valve member is carried by a valve stem 27a which has on its upper end a valve member 28 which cooperates with valve seat 29 in the upper seat sub 23a. Flat 31 are provided on the valve stem adjacent the valve member 28 and a cylindrical piston 32 is provided immediately below the flats which cooperates with the cylinder 33 in the upper seat sub 23a. The valve seat 29 is much smaller than the cylinder 33. Thus, as the valve member 28 comes off its seat, a much larger area, being the piston 32, is exposed to pressure to snap the valve to closed position.

The valve is biased toward open position by a resilient member such as spring 34 compressed between the shoulder 35 on the valve housing and a flange or collar 36 on the valve stem.

Within the valve member 27 and valve stem 27a is a casing-responsive valve. The valve member 27 has a small flowway 37 therethrough. This flowway includes the ports 38 which provide inlets communicating with ports 25 in the housing and the outlet 39 which communicates with the flowway 23 downstream of the seat 26.

The flowway 37 is provided with a valve seat 41 and a valve member 42 which cooperate to control flow through the flowway.

Operation of the valve member 42 is controlled by a pressure charge in the pressure dome 43. This dome is closed in the conventional manner by a suitable bellows 44.

In operation, the bellows valve is closed until it is subjected to a selected pressure. The differential valve remains open until it is subjected to a selected differential range. Thus, with the valve in the hole and the casing under pressure, as is conventional in an unloading operation, the differential valve would in the beginning be closed because the casing pressure would be much greater than the tubing pressure exerted on the valve. However, as the casing pressure reaches a selected value, the casing-responsive valve 42 comes off its seat and fluid is introduced into the tubing from the casing and this fluid rises in the tubing to exert a pressure on the differential valve 27. As this pressure become greater than the value of the casing pressure, less the force exerted by spring 34-, the differential valve will move off its seat. When this occurs, the additional area of the valve member 27 being exposed to casing pressure will snap the differential valve to full open position, seating valve member 28. Upon this event, flow commences through the differential valve and the pressure within the housing 21 drops to tubing pressure because the combined area of ports 25 is less than the area of port 26. Thus, a casing-tubing differential as influenced by spring 34 is exerted across valve 28. The differential valve remains open until the tubing pressure drops to a value which exerts a force which combined with the force of spring 34 is slightly less than casing pressure. In this condition the valve 28 comes off seat 29 and the casing pressure is exerted across piston 32. This snaps the differential valve back to closed position.

It will be noted that the casing-responsive valve 42 would normally be closed while the differential valve is operating, because the pressure to which bellows 44 is subjected woud have dropped from casing pressure to tubing pressure. This is merely a characteristic of the particular design, and whether or not this valve is open or closed is not material, as flow is controlled by passage of fluid through ports 25.

A suitable back pressure valve indicated generally at 45 prevents back flow through the valve in the event of failure of the valve.

It is apparent that this system lends itself to dual completion wells. Both in unloading and working of the well, the level of liquid in each tubing is controlling and each tubing is unoaded and each formation is worked without interference from the other.

Reference is made herein to casing pressure and a cased well is illustrated. The word casing however is meant to include any structure which confines lifting gas and communicates with the flowway for conducting fluid to the surface.

The foregoing disclosure and description of the invention are illustrative and explanatory thereof and various changes in the size, shape and materials, and in the details of the illustrated construction, as Well as in the method and system, may be made within the scope of the appended claims without departing from the spirit of the invention.

What is claimed is:

1. A gas lift system comprising,

a case well having a flow tubing therein,

a plurality of casing pressure-responsive valves spaced along the tubing,

and a plurality of tubing pressure-responsive valves spaced along the tubing with each tubing pressureresponsive valve close enough to a casing pressureresponsive valve to be loaded by liquid introduced into the tubing through said casing pressure-responsive valve while unloading the well, each of said casing pressure-responsive valves and said tubing pressure-responsive valves controlling flow through a separate passageway through said tubing,

said tubing pressure-responsive valves above the working valve providing for introduction of gas into the tubing when the pressure in the tubing at a particular tubing pressure-responsive valve is sufficient to load said tubing pressure-responsive valve.

2. The system of claim 1 wherein the flow passage through the casing pressure-responsive valves is relatively small as compared with the flow passage through the tubing pressure-responsive valves.

3. A gas lift system comprising,

a cased well having a flow tubing therein,

a plurality of casing pressure-responsive valves spaced along the tubing,

and a plurality of differential valves spaced along the tubing with each differential valve close enough to a casing pressure-responsive valve to be loaded by liquid introduced into the tubing through said casing pressure-responsive valve while unloading the well, each of said casing pressure-responsive valves and said differential valves cont-rolling flow through a separate passageway through said flow tubing,

said differential valves above the working valve providing for introduction of gas into the tubing when the pressure in the tubing at a particular differential valve is sufficient to load said differential valve.

4. A gas lift valve assembly comprising,

a housing adapted for connection to a well tubing,

a first flowway through the housing,

a first valve seat across the flowway,

a first valve member cooperative with the first valve seat to control flow' through the first flowway,

a second flowway through the housing,

a second valve seat across the said flowway,

a second valve member cooperative with the second valve seat to control flow through the second flowy,

means responsive to pressure external to said tubing for operating one of said valve members,

and means responsive to tubing pressure for operating the other of said valve members.

5. The gas lift valve assembly of claim 4 wherein the tubing pressure-responsive valve is a differential valve.

6. The gas lift valve assembly of claim 4 wherein one fiowway extends through the valve member controlling the other flowway.

References Cited UNITED STATES PATENTS 3,223,109 12/1965 Cummings 137-155 3,270,765 9/1966 Waters 137-155 3,016,844 1/1962 Vincent 10 3232 3,045,759 7/1962 Garrett et al 103233 3,225,783 12/1965 Stacha 137-155 3,277,838 10/1966 Canalizo 103-232 3,311,126 4/1967 Dudley 103--232 ROBERT M. WALKER, Primary Examiner. DONLEY J. STOCKING, Examiner. W. J. KRAUSS, Assistant Examiner, 

